Nouns are naming words. We use them to give names to people, objects, thoughts, feelings, substances, etc.

María - Mary
mesa - table
alegría - happiness
oro - gold

In Spanish nouns distinguish between masculine and feminine. Generally if a noun ends in "-o" it is masculine and if it ends in "-a" is feminine, although there are many exceptions to this rule. Eg:

Éste es mi niño. - This is my child.

In this example the noun "niño" names a boy.

Ésta es mi niña. - This is my child.

In this example the noun "niña" names a girl.

Spanish nouns also distinguish between singular and plural.

The general rule is to add "-s" to the noun in singular.

una mesa - one table
tres mesas - three tables

If the singular noun ends in "-z" we do its plural en "-ces".
Tengo un pez. - I have a fish.
Tengo tres peces. - I have three fish.

When the singular noun ends in "-s" and it is formed by only one syllable, we add "-es" to form the plural. This rule also applies to nouns of more than one syllable ending in "-s" and with the accent in the last syllable.

No tengo compás. - I do not have a compass.

Yo tengo dos compases. - I have two compasses.

Nouns ending in "-i" with "tilde" or in "-y" do their plural by adding "-es".

el rey - the king
los reyes - the kings

un Israelí - an Israeli
dos Israelíes - two Israelis